Plugs & Mileage

Here's the scenario     The plugs in the E320 were Bosch Supers.     I changed them to Bosch Platinum 4s.     Fuel mileage dropped from 29mpg to 26mpg.
One hypotheseis is that the Platinum 4 plugs require more voltage and so were desaturating the coil. As a consequence, not enough spark for a good burn. Another is that they were too efficient, prompting the computer to input more fuel, thus increasing consumption.
(Last night I changed back to the Supers.)
What are your thoughts on this?
Collin KC8TKA E320/97
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I'm not sure...a 3mpg drop in mileage seems to be within the margin of error. How many miles/tanks did you go through to do the calculation? Same driving conditions on both?
Might it be worthwhile to purchase another set of Bosch Supers and seeing if you get the same mileage?
Or, like me, you could get a diesel and not worry about spark plugs. :)
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Pete Stephenson
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I looked for a diesel but couldn't find one when I really needed a car. A few weeks earlier there as a 300D/2.5 in the area, but not at the right time. If I could trade this car even-up for a diesel, it would be a nice thing. The car just needs that little bit of TLC which will take me a couple of months to work through. But other than that, it's certainly good to drive.
Collin KC8TKA
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29 mpg ought to be verified - seems very high.
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Not really a high value. That was measured for almost 2 months driving to / from work. All highway. Including a cross-country trip to Wisconsin -- 10 hours each way. And my brother's 86 300E got 32 hwy regularly. I can understand 25mpg in city/hwy mixed drivning. But straight hwy can be 29+ with ease.
collin kc8tka
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I am not sure about this 97 E320 engine. My 96 C280 has M104.941 which is inline 6-cylinder, DOHC. I think M104 also has a 3.2 liter version.
My M104 has to use Bosch Super because its spark circuit design includes the plug resistance. Platinum plug has different resistance and will cause misfire.
Cheesehead wrote:

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